In vivo biostability of CVD silicon oxide and silicon nitride films

Low pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD) silicon oxide and silicon nitride films were implanted subcutaneously in a rat model to study in vivo behavior of the films. Silicon chips coated with the films of interest were implanted for up to one year, and film thickness was evaluated by spectrophotometry and sectioning. Dissolution rates were estimated to be 0.33 nm/day for LPCVD silicon nitride, 2.0 nm/day for PECVD silicon nitride, and 3.5 nm/day for PECVD silicon oxide. A similar PECVD silicon oxide dissolution rate was observed on a silicon oxide / silicon nitride / silicon oxide stack that was sectioned by focused ion beam etching. These results provide a biostability reference for designing implantable microfabricated devices that feature exposed ceramic films.